Bioactive Implants

In the Work Area "Bioactive Implants", we are investigating the mechanisms of corrosion of the materials with the aim of modifying and controlling them for clinical applications, thus enabling the use of biodegradable metals as implant material. A further research focus is the characterization of the ongoing immune reactions after implantation of the materials for the assessment of their biocompatibility.

Research Focus

Magnesium based implants

Open-porous implants made of biodegradable magnesium have a major advantage over solid implants: they have a reduced implant volume which creates a lower amount of degradation products and leads to a faster completion of the degradation. However, the implant design needs to provide sufficient initial mechanical stability to fix the broken or osteotomized bone. A novel approach to produce these open-porous and load-bearing scaffolds is liquid-phase sintering or an additive manufacturing method called Laser Selective Melting which we investigated with our partner the Fraunhofer Institute for Lasertechnology in Aachen.

Custom-specific coatings are needed to control the corrosion rate and enhance cytocompatibility to biodegradable magnesium implants. Those coatings are mainly based on immersion techniques. Perfusion-bioreactors have been used to investigate the influence of a changing, dynamic environment on the corrosion of magnesium implants. These results will be compared to samples which have been implanted into in vivo models.

Understanding and controlling magnesium corrosion in vivo. The corrosion rate of magnesium implants can be controlled by the classical production route, namely the use of specific alloying elements, mechanical processing and coatings or surface finishing. However, the biological environment has a dramatic influence on the corrosion rate, which is the main reason for the differences in results of in vitro and in vivo tests with the same material. Perfusion bioreactors are helping to understand at least partly the in vivo situation.

Foreign body response

Biodegradable implants based on magnesium offer several advantages mainly the lack for implant retrieval. However, the degradation products could cause negative side effects. Therefore, biocompatibility has to be proven before clinical use.

Our group established a flow cytometry analysis based marker panel to investigate and better understand the foreign body response to implants particularly with respect to the influence of degradation process on the immune response. For that purpose, permanent (polystyrene, polyetheretherketon) and degradable (pure magnesium) material samples were implanted in in vivo models. After several time points the capsule which has formed around the implants was harvested and the immune cells were isolated by a special single cell preparation protocol. Cells were labeled with specific cell surface antibodies to be analyzed and quantified by flow cytometry. Furthermore, immune cells were quantified in blood samples and the spleen to assess systemic immune reactions.

The cell patterns revealed a comparatively moderate local foreign body reaction in all test groups with an early immigration of granulocytes into the implant side followed by macrophages und T cells. The degradation of the magnesium did not increase the number of inflammatory cells in general indicating a good biocompatibility. However, the role of the increased T helper cells in the test groups treated with pure magnesium has to be investigated in further studies.

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Contact

Prof. Dr. Frank Witte

Charité - Universitätsmedizin Berlin
Berlin-Brandenburg Center for
Regenerative Therapies
Julius Wolff Institute
Charitéplatz 1
10117 Berlin
Germany

Phone: +49 (0)30 450 559 083
Email: frank.witte@charite.de